The invention relates to a device for carrying out surface profilometry measurements on wafers during processing. It also relates to a measurement method implemented by the device.
The field of the invention is more particularly, but non-limitatively, that of the measurement and dimensional control of the devices in the field of microsystems (MEMS) and in microelectronics.
The manufacturing methods implemented in microelectronics generally rely on successive steps of the deposition of layers and etching, which result in the production of components in the form of stacks.
A very high degree of flatness of the layers is often necessary. Thus it is known to implement techniques, in particular optical profilometry, for measuring this flatness.
Among the optical profilometry techniques those called “full-field” are known which make it possible to obtain the shape of a surface directly in one or a small number of measurements. There are in particular interferometry techniques which use interferences between a measuring beam reflected by the surface to be measured and a reference beam. Different interferometer architectures are possible, some of which are known by the names Linnik, Mirau, Michelson or Fizeau interferometers.
Optical interferometry techniques are also known based on point-to-point distance measurements with a spot measuring beam which scans the surface. The detection techniques implemented in this case can in particular comprise the confocal, chromatic confocal techniques, or those based on interferometry or low-coherence interferometry (with broad-spectrum sources). They have the drawback however of being much slower than the full-field techniques.
A constraint common to all these techniques is that the reflectivity of the surface to be measured at the working wavelengths must be high in order to obtain good measurements. It is also necessary for the measurements not to be disturbed by stray reflections on the buried layers. Thus, wavelengths are generally used that do not penetrate into the materials, or only slightly (visible wavelengths for silicon), or, when the layers to be measured are transparent in the visible spectrum, metal deposition is carried out thereon beforehand (tantalum).
In certain situations, it is necessary to measure and characterize the flatness of layers that cover components or chips already produced, facing these components. The problem that then arises is that these components are not visible from the measurement face. It is thus difficult to attach or reference the flatness measurements to the exact position of these components, without using a priori design information which is inevitably inaccurate.
A purpose of the present invention is to propose a profilometry measurement device and method making it possible to carry out measurements of the shape of a surface that are registered or referenced accurately with respect to components buried in the wafer or at least located beneath the surface to be measured.
A purpose of the present invention is also to propose a profilometry measurement device and method making it possible to carry out measurements of the shape of a surface within a frame of reference linked to components buried in the wafer or at least located beneath the surface to be measured.